Color printing typically involves interaction between a customer, a photographer, a pre-press house, and a printer. The process generally begins with a photography session or "photo-shoot", during which photographs of the desired scene are taken. The photographic film typically used is of the type for producing color transparencies, or slides, because using negatives with color prints would add an extra level of complexity, loss of sharpness and color distortion to the process. Once approved, the developed transparencies are then sent to the pre-press house where the required color separation process is performed and a set of film, typically one for each subtractive color (cyan, magenta, yellow and black), known as half-tones are produced. The acceptability of the color separation can be checked by producing a positive proof from the half-tone films. The positive proof is indicative of how the final printed product will look. Typically, the positive proof is not produced by an offset press because of the substantial cost of configuring the offset press, which is usually only justified if it is determined in advance that the customer will be satisfied with the printed product. Instead the proofs are often produced by a manual process requiring semi-skilled labor and costs of materials. If the customer approves the proof, then the half-tones are sent to the printer. If the proof is not acceptable, then the color separation must be redone with new parameters, or alternatively, a new photo-shoot is required. The proof becomes a contract specification for the printer, i.e. the printer must match the final print to the proof.
One problem with this process is that it requires skilled craftsmen at the pre-press house to make a subjective judgment, typically through an iterative process, to achieve what they consider to be a good color reproduction of the photographic original (the transparency) taking into account corrections requested, or presumed to be desired, by the customer. Another problem is that the color separation process is expensive and requires expensive equipment, e.g., expensive scanners for scanning the slides. Yet another problem with this process is that the proof of half tones is not available for review and approval by the customer until well after the photo-shoot photography session. Since slight errors of lighting or exposure can produce small but unacceptable color cast or tonal errors, even the best of several shots of the same subject often requires correction in the scanning and separation process. Such editorial improvements upon the original can only be accomplished with the human judgment of a trained operator, and may be unacceptable to the customer.
In order to confirm and insure that the customer is satisfied with the composition and lighting of the photographs taken during the photo-shoot, often, during the photo-shoot the photographer takes an instant photograph of the scene, typically using self-developing film of the type manufactured and sold under the trademark Polaroid by the Polaroid Corporation of Cambridge, Mass., prior to exposing the slide film. However, since both the customer and the photographer know that several corrections and human judgments will be made during the separation process, there has been no motivation to make the Polaroid instant photograph strongly resemble the desired printed product.
Although the theoretical possibility exists for converting reflection originals for accurate reproduction by mechanical processing means, without the trained human who traditionally creates the match, this possibility has not been pursued because:
1. The heavily predominant practice is to use transparency materials for originals. When reflection materials are involved, they are usually pan of a mixed job that also involves transparencies. PA1 2. When reflection materials are intended for color reproduction, they frequently require correction as stated above, and so exact reproduction of the color original is not desirable. PA1 3. The range of colors that can be produced in a particular printing process are the "in gamut" colors, while those outside the process are "out of gamut" colors. Gamut mis-match between original and reproduction, particularly with respect to the extremes of the neutral scale, requires that for good results, even the in-gamut colors must be reproduced without exactly matching conventional colorimetry. Conventional color science does not teach how to deal with this problem effectively. PA1 4. Unless all, or very nearly all, of the images in a job can be processed mechanically, much of the attraction of a mechanized procedure is lost. PA1 5. Since the reflection original cannot be trusted to represent the customer's desires, the advantage of being able to substitute it for a separation proof is lost.